The present invention relates to a light source device for an image processor which converts a picture image detected by an industrial television (ITV) into a binary numeral for further processing, and more particularly to a light source device of an image processor adapted to detect a solder leveler formed on a print circuit board.
The image processor which converts a picture image signal picked up by the ITV into a two-value data comprising a high level signal and a low level signal (1 and 0) is now used in various technical fields. In an automatic mounting system of electronic devices, the image processor is used for detecting the mounting positions of the devices and positions of standard marks on a print circuit board.
Referring to FIG. 1, showing an example of a conventional image processor, an ITV camera 2 is mounted on a robot 1 at an appropriate vertical position dependent on a focal length of the camera. A light source device 11 is mounted on the ITV camera 2 around a lens barrel 4 thereof. The light source device 11 has a light source such as a cold-cathode tube and/or LEDs which emits light, and a diffusing plate for transmitting and diffusing the light. In order that diffused light transmitted through the diffusing plate may have a sufficient quantity of light, a light source capable of emitting a relatively large quantity of light is selected.
The diffused light from the light source device 11 is projected onto a standard mark 10 formed on a print circuit board 3. However, only the light within a range indicated by dot-dash lines 11a between the light source device 11 and the standard mark. 10 in FIG. 1 is applied to the standard mark 10. The direction of light beam to be projected on the mark 10 is the direction included in the range between the lines 11a.
Since the standard mark 10 is made of a conductive material such as a piece of copper foil, the surface thereof is flat. Therefore, in the case where the position of the mark 10 is detected, a comparatively sufficient quantity of light is reflected on the flat surface, although the light in the only small range defined by the lines 11a is projected on the mark. Consequently, an appropriate picture image can be obtained by the ITV camera. Hence no serious trouble occurs.
The image processor is also used for detecting the position of a conductive member coated with solder, that is, a solder leveler. The thickness of the solder coated on the conductive member is often irregular and hence the surface of the solder leveler is uneven. Namely, as shown in FIG. 4, the surface of a solder leveler 12 formed on the standard mark 10 is uneven in most cases. Moreover, due to the surface tension of the molten solder, the surface of the leveler is smooth. Therefore, diffused reflection on the surface occurs very little. Consequently, the directions of the reflected light is determined by the incident angle of each light beam. Hence, depending on the inclination of the surface of the solder leveler, or the existence of pinholes, the light reflected on the surface, for example, at a point B shown in FIG. 4 is hardly detected by the ITV camera 2. As a result, the detected image data for the solder leveler 12 recognized by the image processor fails to show the portion corresponding to the point B.
More particularly, as described above, the light applied to the solder leveler 12 from the conventional light source device 11 is in the range between the lines 11a in FIG. 1. Showing light as being applied to a point A in FIG. 4, the light within a hatched area defined by lines 11b is projected on the point A. An incident light Ai reflected on the point A becomes a reflected light Ao which is directed toward the ITV camera 2. If the inclination of the solder surface becomes larger than that of the point A, the light Ai does not reflect to the ITV camera. In order to reflect to the ITV camera on such a large inclination surface, the light Ai must be applied at a larger incident angle. In other words, a more inclined direction than the illustrated angle of the light Ai can be picked up by the camera. However, since the light having a maximum incident angle is the incident light Ai in the conventional light source device 11, none of the beams reflected on such a steep surface are fed to the ITV camera 2, so that the image processor forms an incomplete image data having gaps.
As described above, if the inclination of the surface of the solder leveler is large or pinholes are formed on the surface, the quantity of light fed to the ITV camera decreases. Hence the images are darkened, thereby further causing the gaps to be formed when converted into a two-value data.
When the image processor recognizes such an incomplete image, the detected contour or the center of the image inevitably differs from the actual contour or the correct center of the object, thereby causing error in the measurements. In order to solve such a problem, there has been proposed an image processor provided with a system where the gaps in the image are compensated through an exclusive operation so as to obtain a full image. However, not only is such an image processor expensive, but in many cases, it is difficult to detect the gap included in the image. Hence the conventional image processor system is insufficient to eliminate the defect.